How to change inflow velocity attributes randomly while animation
You can do this with F-Curves


Insert keyframe for inflow (press I hovering over the attribute).
Open Graph editor.
Add the F-Curve Modifier: Noise (Shift+Ctrl+M).


Or a little more complicated with a Driver


Add a Driver to the Attribute (Ctrl+D hovering over the attribute ‣ Add Driver ‣ Manualy Create Later)
Open Graph editor
Go to Drivers Mode
Select the Curve of the Attribute you want to Animate
Go to Drivers Tab in Toolshelf
Set the Driver to noise.random()